1. Field of the Invention
The invention relates to a waveguide for receiving or radiating electromagnetic radiation, in particular light, to the use of such a waveguide as well as to a method for manufacturing such a waveguide.
2. Description of the Related Art
For a series of technical and medical uses it is necessary to uniformly illuminate a cavity. For spherical cavities this may be effected by an isotropic radiation source which is located in the center of the cavity. If the radiation source may not or is not to be brought itself into the cavity, such as e.g. with the examination and therapy of hollow organs in the human body, an optical waveguide which is provided at its end with an isotropically radiating scatter body may guide the light or the radiation from the source into the inside of the cavity and here radiate isotropically.
One example of the use of such a device for the uniform illumination or radiation of the inner surface of a spherical human hollow organ is integral photodynamic therapy (PDT) in a urinary bladder with multifocal tumor occurrence. For the success of this therapy it is necessary e.g. for the inner wall of the urinary bladder which is stabilized in spherical manner to be radiated homogeneously. A non-homogeneous intensity distribution of the light radiation directed onto the inner wall of the urinary bladder at locations with a low radiation dose leads to no or an inadequate destruction of the photo-sensitivised tumour tissue.
All isotropically radiating scatter bodies known up to now have a ball of light-scattering material located at the end of an optical waveguide. See, for example, U.S. Pat. Nos. 5,119,461; 5,074,632; 5,190,536; and 6,096,030. With this known device, hereinafter called an applicator, the photons in the ball exiting the optical waveguide are scattered many times in a diffuse manner so that they lose their original direction. With a suitable choice of the composition of the scatter medium, this leads to approximately spherical radiation characteristics of the applicator. In order to also radiate sufficient light intensity in the direction of the optical waveguide, i.e. in the proximal direction and thus to reduce shadowing effects by way of the optical waveguide, the ball diameter of the scatter body is about four times larger than the diameter of the optical waveguide. This entails the following disadvantages.
The constructional shape of the known applicator, at the connection location of the optical waveguide to the spherical scatter body particularly with small applicator sizes creates problems with regard to the mechanical stability. Furthermore the diameter of the optical waveguide limits the maximum power which may be transmitted into the cavity. With spatially incoherent radiation the ability to focus is limited and only a sufficiently large optical waveguide permits an effective transmission of the light. With laser radiation which on account of its coherence and monochromatic property may be focussed very well, the destruction threshold of the optical waveguide or the connection of this to the scatter body limits the transmittable power. In both cases the power able to be transmitted by the optical waveguide increases with its cross-sectional area. It is therefore desirable to adapt the diameter of the optical waveguide as much as possible to the respective cavity diameter or access channel to the cavity. With the scatter bodies of the applicators described in the state of the art which guarantee a largely homogeneous illumination of the cavity, the diameter of the guiding optical waveguide is limited to a quarter of the diameter of the scatter body and thus of the diameter of the access to the cavity.
In medicine and technology spherical or similar cavities may be reached only via a relatively small access channel. With the above-mentioned photodynamic therapy (PDT) of the urinary bladder, the diameter of the spherical scatter body of the applicator should be ≦3 mm on account of the narrow urethra. At the same time with the applicator of the state of the art the diameter of the optical waveguide would have to be limited to ≦0.75 mm. By way of the thus relatively low optical waveguide cross section and by way of the high scatter coefficients of the scatter body, already with relatively low laser powers of ≦3 W at the exit area of the optical waveguide there occur such high radiation intensities that the heating produced with this may lead to a destruction of the applicator.
DE 3 941 705 C2 describes a device for the homogeneous radiation of cavities which consists of a balloon catheter in which the conically pointed end of the optical waveguide is positioned centrically to the middle of the balloon in the catheter. The balloon is filled with a diffusely scattering liquid and at the same time assumes a spherical shape. Since the actual applicator only first appears at the user on filling the balloon, there lacks an exact quality control with regard to the quality of the radiation characteristics of the radiation applicator. For the user it is also cumbersome and difficult to fill the balloon with absolutely no bubbles. Furthermore the balloon may be perforated on introduction into the cavity. Since yet an additional channel must be provided for filling, and the balloon takes up some space even in the non-filled condition, here too one may not use the complete diameter of the access channel for the diameter of the optical waveguide.